Bolometer

A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance.

On the other hand, compared to more conventional particle detectors, they are extremely efficient in energy resolution and in sensitivity.

The first bolometers made by Langley consisted of two steel, platinum, or palladium foil strips covered with lampblack.

The strips formed two branches of a Wheatstone bridge which was fitted with a sensitive galvanometer and connected to a battery.

He also discovered new atomic and molecular absorption lines in the invisible infrared portion of the electromagnetic spectrum.

Their use as particle detectors was proposed from the beginning of the 20th century, but the first regular, though pioneering, use was only in the 1980s because of the difficulty associated with cooling and operating a system at cryogenic temperature.

Recent progress includes the refinement of a tomographic reconstruction algorithm, which leans on the principle of relative gradient smoothing (RGS) of emission profiles.

This has been effectively applied to the W7-X hydrogen discharges powered by electron cyclotron resonance heating (ECRH).

The inclusion of a 50 nm carbon layer is strategic, enhancing the detection efficiency for low-energy photons.

These detectors are notably attuned to impurity line radiation, covering a spectrum from the very ultraviolet (VUV) to soft x-rays (SXR).

Infrared radiation from a specific range of wavelengths strikes the vanadium oxide or amorphous silicon, and changes its electrical resistance.

640x512 VOx arrays are commonly used in static security camera applications with low shock resistance requirements.

The hot electron bolometer (HEB) operates at cryogenic temperatures, typically within a few degrees of absolute zero.

A dc bias current is applied to the resistor to raise its temperature via Joule heating, such that the resistance is matched to the waveguide characteristic impedance.

Image of spiderweb bolometer for measurements of the cosmic microwave background radiation.
Spiderweb bolometer for measurements of the cosmic microwave background radiation . Image credit: NASA/JPL-Caltech .
Conceptual schematic of a bolometer.
Conceptual schematic of a bolometer . Power, P , from an incident signal is absorbed and heats up a thermal mass with heat capacity , C , and temperature, T . The thermal mass is connected to a reservoir of constant temperature through a link with thermal conductance , G . The temperature increase is Δ T = P / G and is measured with a resistive thermometer, allowing the determination of P . The intrinsic thermal time constant is τ = C / G .